diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 8bd2059d..aee8bab5 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -52,6 +52,12 @@ jobs:
     - name: Run pytest (not unit, including running notebooks)
       run: |
         pytest --verbose -m 'not unit' tests/
+    - name: Save build log
+      uses: actions/upload-artifact@v2
+      if: always()
+      with:
+        name: ${{ matrix.os }}-${{ matrix.python-version }}-build-log
+        path: build-log.jsonl
     - name: Save build error logs
       uses: actions/upload-artifact@v2
       if: failure()
diff --git a/build.py b/build.py
index 770a13b4..453060d6 100755
--- a/build.py
+++ b/build.py
@@ -66,6 +66,7 @@
 from collections import namedtuple
 from datetime import datetime
 import glob
+import json
 from io import StringIO
 import logging
 import os
@@ -113,6 +114,18 @@
 _log.setLevel(logging.INFO)
 
 
+def _log_json(path='build-log.jsonl', **kwargs):
+    import platform
+    data = dict(
+        kwargs,
+        platform=platform.platform(),
+        python_version=platform.python_version(),
+    )
+    json_str = json.dumps(data, default=str)
+    with Path(path).open('a') as f:
+        print(json_str, file=f, sep='\n')
+
+
 # This is a workaround for a bug in some versions of Tornado on Windows for Python 3.8
 # this is the recommended fix for this according to e.g. https://github.com/tornadoweb/tornado#2608
 # it should be revisited with python>=3.9 or if a fix is implemented by e.g. Jupyter
@@ -738,6 +751,12 @@ def convert(self, id_, job, log_q) -> ConversionResult:
         self.log_info(
             f"Convert notebook name={job.nb}: end, ok={ok} duration={duration:.1f}s"
         )
+        _log_json(
+            id=id_,
+            notebook=job.nb,
+            ok=ok,
+            duration=duration,
+        )
 
         return self.ConversionResult(id_, ok, converted, why, job.nb, duration)